We plan to study the physiologic mechanisms involved in initiation and recovery from apneic spells. Special emphasis is given to apnea associated with upper airway obstruction (obstructive and mixed apnea). First, we will study mechanical and neuromuscular factors relevant to pharyngeal airways maintenance in anesthetized living and in dead rabbits. Mechanical effects of stimulating contraction in the genioglossus, sternohyoid, sternothyroid, and geniohyoid muscles will be studied. Also, effects of maturation on intrinsic compliance of the pharyngeal airway and hyoid bone will be studied. Second, in human infants with tracheostomies, respiratory responses to suction pressure within the upper airway, as well as vibratory and muscle stretch stimuli, will be studied. Effects of such stimuli on electrical activity of upper airway muscles and diaphragm, inspiratory air flow, tidal volume and breathing frequency will be evaluated. In these infants the relationship between airway closure and airway stimuli will be assessed. Third, in healthy preterm infants, and those with idiopathic apnea, we will assess pharyngeal airway stability by determining upper airway closing pressures and responses to a very brief period of nasal occlusion during sleep. Furthermore, in such infants we plan to investigate the mechanisms involved in apneic spells associated with swallowing and the possible relation of such spells to airway obstruction, airway secretions, and gastric fluid. These studies are viewed as relevant to the maturation and development of respiratory control in man and to the clinical syndromes of long-term tracheostomy, apnea of prematurity, obstructive sleep apnea, and sudden infant death syndrome.